Episode Behind the Scenes


When phasers are fired at the Doomsday Machine they are shown radiating out from their point of origin like spokes on a wheel, yet when the scene changes to show the two beams striking their target the beams are now parallel. (This is fixed in the remastered 2007 version.)
On the Constellation, when Captain Kirk tells Scotty to check the phasers and see if they've been fired, he inadvertently says "fireds."
If one counts the fan-made series "Star Trek: New Voyages" as canonical, then Commodore Decker survived his suicide run at the doomsday machine and was transported back in time to the 20th century as revealed in the episode "In Harm's Way".
James Doohan briefly loses his "Scotty' accent when wishing Kirk good luck before beaming off the Constellation.
When entering the Doomsday Machine, both the shuttle and the Constellation are almost identical in size as compared to the Machine. (This is corrected in the remastered 2007 version.)
When the Enterprise was shown from the left, the starboard (right) side running light was green instead of red and the "NCC-1701" was reversed.
When Kirk pressed the self-destruct for the Constellation, it was set for 30 seconds but it took 70 seconds for it to be destroyed.
Scotty is attempting to jury rig the Constellation. He advises Kirk that one particular set of repairs "will make the ship almost impossible for one man to operate". Inasmuch as the normal complement is over 400 men and women, one assumes the ship is "almost impossible" for one man to operate when everything is working! It's likely that a wrecked ship like the Constellation would be darn near impossible for even it's full complement to operate. (Indeed, in another episode, The Ultimate Computer, Kirk believes that a crew of 20 is too few to operate the Enterprise even with a state-of -the-art automation system installed).
The Doomsday Machine is made of solid neutronium, a material so dense that a teaspoon weighs tons. And yet, in several scenes, the background stars can be seen through the machine! Most likely, this is because the machine was a matte painting on a transparent background, superimposed over the star background in post production. Anywhere the color is dark (i.e. not much paint), the stars can be seen through. (This is fixed in the remastered 2007 version.)
Richard Compton, who plays Washburn, would later become a director for "Star Trek: The Next Generation".